The invention relates to a method of manufacturing a semiconductor device with a pn junction, whereby an epitaxial layer with a first zone of a first conductivity type and a second zone of a second conductivity type opposed to the first is provided on a silicon substrate, the pn junction being formed between said second and first zones.
A pn junction manufactured in this way is used in various types of semiconductor device. Thus the pn junction may be used, for example, for manufacturing a so-called varicap diode. The pn junction in such a diode is reverse biased during use by a reverse voltage across the pn junction. The region around the pn junction is depleted of charge carriers then and acts as a dielectric of a capacitance. The value of this capacitance depends on the reverse voltage and on the doping concentration of atoms of the respective conductivity type in the semiconductor material. The pn junction is accordingly used for obtaining a certain capacitance-voltage (CV) relation. It is alternatively possible, however, to influence the properties of other pn junctions, such as a base-emitter pn junction of a bipolar transistor, or the properties of a zener diode by means of the method.
U.S. Pat. No. 3,638,301 discloses a method of the kind mentioned in the opening paragraph whereby a varicap diode is manufactured. In this method, a p.sup.- -type epitaxial layer is provided on the silicon substrate, whereupon dopant atoms are provided in the epitaxial layer through diffusions so as to form a first, n.sup.+ -type and a second, p.sup.+ -type zone.
The known method described has the disadvantage that it is not very flexible. The capacitance-voltage (CV) characteristics of varicap diodes manufactured by the known method can be varied to a very limited degree only. It is furthermore found to be necessary in practice to take a number of additional measures if very high uniformity requirements are to be met. Thus the diffusion for making the second zone is carried out for too short a period initially. Varicap diodes on a substrate are then tested and subsequently brought up to specification in one or several post-diffusion and measurement steps. Subsequently, all varicap diodes on the substrate are measured once more and the varicap diodes are selected for final mounting by an intricate calculation method, a so-called matching algorithm.